When converting a device-dependent color space that is dependent on the color reproduction characteristics of a device, for example, when converting a color value in a first device-dependent color space to a color value in a second device-dependent color space, color matching of color value is performed through the agency of a device-independent color space that is independent of any device, so as to match color reproduction in the color space prior to conversion and the color space subsequent to conversion.
During conversion of the color space of a color value, typically, an operation using a matrix is performed, for example, using a first matrix when converting the color space of the color value from a first color space to a device-independent color space, and using a second matrix when converting the color space of the color value from a second color space to a device-independent color space. When converting the color space of a color value from a first color space to a second color space, in order to accelerate the conversion process, a third matrix calculated in advance on the basis of the first matrix and the second matrix is used to perform conversion processing of the color space of the color value.
However, where the effective number of decimal places of the third matrix calculated from the first matrix and the second matrix has not been rounded, so that a large effective number of decimal places is retained, there is the problem that a long time is required for color space conversion processing.
On the other hand, if, in order to accelerate the conversion process, the effective number of decimal places of the third matrix has been rounded, even if the white points of the first and second color spaces should match in the device-independent color space, the color value based on the second color space obtained by converting the color value of the white point based on the first color space using the third matrix will not match the color value of the white point based on the second color space, that is, there is the problem of inferior color space conversion accuracy. Typically, human visual perception is sensitive in the colorless region that contains the white point, so even slight deviation in color value will be apparent to the eye, so that it becomes impossible to achieve correct color reproduction.
Also, where white point data in the first color space and white point data in the second color space originally do not match in the device-independent color space, there is the problem that even if conversion process accuracy using the third matrix is raised, the white point in the first color space and the white point in the second color space will not match, so a color space conversion process satisfactory to the user cannot be performed.